Precision resistance element and method of making the same



United States Patent 3,324,049 PRECISION RESISTANCE ELEMENT AND METHODOF MAKING THE SAME Curtis L. Holmes, Elkhart, Ind., assignor to CTSCorporation, Elkhart, Ind., a corporation of Indiana No Drawing.Continuation of abandoned application Ser. No. 276,064, Apr. 26, 1963.This application Feb. 18, 1966, Ser. No. 528,379

15 Claims. (Cl. 252-514) The present application is a continuation ofour copending application entitled Precision Resistance Element, Ser.No. 276,064, filed Apr. 26, 1963, now abandoned, which application is inturn a continuation-in-part of our application entitled, ElectricalResistor and Method of Making the Same, Ser. No. 169,355, filed Jan. 29,1962, now abandoned.

The present invention relates to resistance elements and, moreparticularly, to an improvement in the stability of a precisionresistance element of the cermet type such as a fixed volumetricresistance element or a thin film resistance element fired onto asurface of a substrate. Recently, with the increasing trend towardminiaturization, the demand for resistance elements having improvedcharacteristics has multiplied mauyfold. The introduction of the cermetresistance element, i.e., a resistance element formed of at least onemetal such as one of the noble metals, or an oxide thereof, in a fineparticle size, i.e., a size of 325 mesh or smaller, preferably of amolecular size, dispersed ina glass or suitable ceramic material, hasenabled manufacturers of resistance elements to produce 'a precisionresistance element having a stable shelf life, low no-load humiditycharacteristics and the like.

Two of the problem areas in the manufacture of a cermet resistanceelement which have continued to plague the manufacturers are (a) theditficulty in controlling the temperature coefiicient of resistance,that is, the percentage change in resistance with respect to a change intemperature and b) the stability of a cermet resistance element atvarious operating loads with respect to time. The temperaturecoeflicient of resistance of a cermet resistance element has been keptto a minimum, e.g., by combining a conductive material having a positivetemperature coefiicient with a conductive material having a negativetemperature coefficient. Theoretically, the temperature coefiicient ofresistanceof a resistance element could be maintained at substantiallyzero if the percentages of the conductive materials or particles couldbe precisely controlled in the end product. Other means well known inthe art are also employed. The stability of a cermet resistance elementhas heretofore remained a problem regardless of what ingredients,elements or compounds were added to the electrically'conductiveparticles or conductive fraction of the mixture employed in producingthe resistance element. Based on the prior art, it has been acceptedpractice to add one or more metals or the oxide thereof to theelectrically conductive portion of a resistance element without changingthe form of the metal or oxide thereof, e.g., metal oxides have beencombined together in various proportions to produce a resistance elementhaving a desired negative temperature coefiicient. The metal oxides,however, always remained in their original form whether it becrystalline or amorphous. The addition of a metal or an oxide thereof tothe conductive fraction of a cermet resistance element has beenineffective since such addition substantially reduces the ohmicresistance of the resistance element without changing the stabilitythereof. It would, therefore, be desirable to produce a ceramicresistance element having an extremely high stability at various loadsand overloads with respect to time without substantially altering theohmic resistance, i.e., by dissolving the additive in the glass therebystructurally combining the additive with the glass.

Accordingly, it is an object of the present invention to provide acermet resistance element having higher stability than heretoforeavailable. Another object of the present invention is to improve thestability of a cermet resistance element by adding small percentages ofmanganese oxide and/or cupric oxide to the admixture of metal particlesand powdered glass employed in making cermet resistance elements. Afurther object of the present invention is to control the temperaturecoeflicient of resistance of a cermet resistance element by adding aspecific ratio of manganese oxide and cupric oxide to the glass employedin the resistance element. Still another obect of the present inventionis to improve the stability of a cermet resistance element by addingsmall amounts of cupric oxide and/or manganese oxide into the rawmaterials employed in preparing the glass thereby dissolving the oxidein the glass. Further objects and advantages of the present inventionwill become apparent as the followmg description proceeds, and thefeatures of novelty which characterize the invention will be pointed outwith particularity in the claims annexed to and forming a part of thisspecification.

The novel compositions of the present inventions are formulated byadding small percentages of cupric oxide and/or manganese oxide to theglass employed in the preparation of cermet resistance elements.Preferably the oxide of copper and/or manganeseinitially in crystallineform is thoroughly admixed with the raw materials employed in preparingthe glass. Whether the oxide of copper and/ or manganese is added to theraw materials forming the glass or after the molten glass is fritteredand ground to a powder is not important so long as the admixture iseventually fired at a temperature sufiicient to fuse the powdered glasscausing the oxide of copper and/ or manganese to dissolve in the glassand structurally become a part of the glass. An organometallic compoundin solution, e.g., a ruthenium resinate, is preferably combined with thepowdered glass containing small amounts of the oxide of copper and/ ormanganese to produce a precision resistance element having improvedstability, i.e., a re sistance element having a very small change inohmic resistance when subjected to various loads and overloads for aconsiderable period of time. I

It is to be understood-that the conductive fraction of the resistancematerial initially need not be an organometallic and can be anorganosol, e.g., ground particles colloidally dispersed in an organicliquid. It has been found, however, that organo-metallic compounds insolution such as metal resinates, glycinates, etherates, esterates, andnapthanates are preferable since the metal particles are in molecularform and may be readily admixed with the powdered glass. As to theconductive fraction, noble metals and/or the oxides thereof such asgold, silver, platinum, palladium, rhodium, iridium, osmium, andruthenium are preferable although other metals can be used.Procedurally, and as indicated in the examples, various glasscompositions may be utilized, the type of glass not being critical tothe practice of the invention. Further, various changes in the glasscomposition can be made to alter the fusion temperature, coefiicient ofthermal expansion, fluidity, solubility and the like by a person skilledin the ceramic art to produce a particular desired characteristic.Generally, if the particular glass utilized in the preparation of thecermet resistance element yields a cermet resistance element having anegative temperature coefficient and, it is desirable to make morepositive the temperature coeflicient, 'the'n cupric oxide is admixedwith the glass since cupric oxide tends to yield a positive temperaturecoefficient. On the other hand, if it is desirable to increase furtherthe negative temperature coefiicient of the element, then manganesedioxide is admixed with the glass. If the cermet resistance element hasa low temperature coeflicient, then the ratio of manganese oxide andcupric oxide added to the glass is controlled to prevent a change in thetemperature coefficient.

The formula for the glass used in the practice of the present inventionmay be any one of several ordinarily used in the art. An example of theraw materials employed in a particular glass formula is as follows:

Raw materials: Percent B 12 Bi203 PbO 66 SiO 11 In order to assure thatthe oxide of copper and/ or manganese becomes thoroughly dissolvedthroughout the glass structure and forms a part thereof, it ispreferable that the oxide of copper and/ or manganese be thoroughlyadmixed with the above raw materials. After a batch of the raw materialsand the oxide of copper and/ or manganese have been thoroughly admixedwhile in a dry state, the batch of the raw materials is placed into aceramic crucible and heated until a molten glass is formed. When thebatch of the raw materials employed in making the glass is heated to amolten mass, the 0xide of copper and/ or manganese loses its originalcrystalline or amorphous form by dissolving and becoming a part of theglass structure. The molten glass is then poured into water at whichtime it solidifies and fritters, the solid particles being commonlyreferred to as glass frit. The glass frit is then ball milled to about325 mesh in size. Each of the noble metals or the oxides thereof is alsomilled to a fineness less than 325 mesh in size. The oxide of copperand/ or manganese eventually dissolves and becomes a part of the glassstructure even if the oxide of copper and/or manganese is admixed withthe glass after it is ground to a powder. Although it is believed thatthere is less homegeneity of the oxide of copper and/or manganese in theglass by adding the oxides thereof to the powdered glass instead of tothe batch of the raw materials forming the glass, the end I result issubstantially the same. This is further substantiated by testsindicating that there is substantially no change in the ohmic resistancewhen an oxide of copper and/or manganese is added to the raw materialsor to the powdered glass. There is, however, a definite improvement inthe stability regardless of when the oxide of copper and/or manganese isdissolved in the glass. Moreover, the oxide of copper and/or manganesecan be admixed with one of the noble metals, e.g., ruthenium, and thenadmixed with the powdered glass to produce a cermet resistance elementhaving improved stability. When the oxide of copper and/or manganesebecomes a part of the glass structure, it is no longer conductive and,therefore, does not substantially affect the ohmic resistance. It does,however, decrease the ohmic resistance somewhat since the additivespermit a finer dispersion of the conductive fraction in the glass.

The present invention will be more completely understood by reference tothe following examples. In each instance, all parts and percentages areby weight, unless otherwise specified. It is to be noted that thestability of a cermet resistance element comprising a glass notcontaining an additive of an oxide of copper and/ or manganese was suchthat the percent change in ohmic resistance after a 72 hour extendedoven test at 200 C. was 2.2 percent.

EXAMPLE I Percent Ir 1 Flint 49 Glass 49 M1102 1 The MnO was added tothe batch of raw materials employed in making the glass and, after theglass was frittered and ground to the proper particle size, the Ir beingpresent in a 4 percent concentration in an iridium resinate, the flintwas added to the glass to produce a precision volumetric resistanceelement having a percentage change in ohmic resistance of only 0.30percent after a 72 hour extended oven test at 200 C. Exhaustive testshave indicated that the 72 hour oven. test at 200 C. is comparable to a1000 hour load life test at C.

EXAMPLE II Composition II was the same as the composition in Example Iexcept that the percent of MnO was increased from 1 percent to 2.5percent. Aft-er a 72 hour extended oven test at 200 C., the percentchange in ohmic resistance was calculated to be 0.15 percent.

EXAMPLE III Percent Ir .7 Ru .3 Flint 49.0 Glass 49.0 MnO 1.0

EXAMPLE IV Composition IV was the same as the composition of Example IIIexcept that the amount of MnO was increased to 2.5 percent. The percentchange in ohmic resistance after a 72 hour extended oven test at 200 C.was 0.15 percent.

EXAMPLE V Percent Ir .7 Ru .3 Flint 49.0 Glass 49.0 M1102 .5 CuO .5

Composition V was the same as the composition in Example III except thatthe amount of MnO Was changed to .5 percent and .5 percent of CuO wasadded. The percent change in ohmic resistance after a 72 hour extendedoven test at 200 C. was 0.11 percent.

Composition VI was the same as the composition of Example V except thatthe amount of MnO was increased to 1.5 percent and the amount of CuO wasincreased to 1 percent. The percent change in ohmic resistance after a72 hour extended oven test at 200 C. was .20 percent.

EXAMPLE VII Percent Ir .7 Ru .3 Flint 47.0 Glass 47.0 Mnoz 5-0Composition VII was the same as the composition of Example III exceptthat the MnO was increased to 5 p rcent. The percent change in ohmicresistance after a 72 hour extended oven test at 200 C. was .13 percent.

EXAMPLE VIII Composition VIII was the same as the composition of ExampleVI except that Ru and Pt were employed instead of Ir and Ru. After a 72hour extended oven test at 200 C., the percent change in ohmicresistance was .16 percent.

In the above compositions, the fllint was used solely to give the fixedvolumetric resistance element sufiicient body. It is to be understoodthat other refractory materials besides flint may be employed inpreparing and producing fixed volumetric resistance elements as recitedin application Ser. No. 169,355, e.g., alumina, beryllia, chromic oxide,feldspar, kaolin, silica, titania, zinc oxide and zirconia. If thefiller material, e.g., flint, is deleted from the resistance element,the ingredients may be cast or molded by means well known to a personskilled in the art, for example, by heating the ingredients to atemperature above the softening point of the glass while in a mold. Itis to be understood that the above compositions for the improvedstability resistance elements can be of the thin film type, the thinfilm resistance element being of the same composition except that asuitable screening agent is employed instead of the filler in order toscreen the mixture onto the surface of a substrate. Preferably, theconductive fraction of the resistance element, that is, the metalparticles such as one of the noble metals should be in the range of .5to 20 percent by weight of the total ingredients used.

Regardless of whether the cermet resistance element is of the fixedvolumetric type or of the thin film type, the element is fired attemperatures sufficient to fuse the glass containing the additives forstabilizing the ohmic resistance and the noble metal particles dispersedtherein to form a precision cermet resistance element. It has beenascertained by exhaustive tests that even 40 percent of Mn0 and/or CuOcan be added to the glass to improve the stability of the resistanceelement without adversely affecting the characteristics thereof;however, smaller amounts of MnO and/or CuO, such as 1 to 2 percent aremost effective in producing the greatest improvement in stability. Asshown by the examples, further additions of MnO and/or CuO show onlyslight improvement in the stability. It is to be understood that theabove examples are merely illustrative and not restrictive. Moreover,the present invention may be susceptible of embodiment in other modifiedforms and that all such modifications which are similar or equivalenthereto come equally within the scope of the claims appended hereto.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A cermet resistance material comprising about 40 to 99 percent byweight of a ceramic glass, .5 to 20 percent by weight of at least one ofthe noble metals selected from the group consisting of Ag, Au, Pd, Pt,Rh, Ir, Os, and Ru in a finely divided state, and .5 to 40 percent byweight Of M1102.

2. A cermet resistance element comprising fine particles of at least oneof the noble metals selected from the group consisting of Ag, Au, Pd,Pt, Rh, Ir, Os, and Ru dispersed in a fused glass, at least .5 percentby weight of M110 dissolved in the glass, and at least one of therefractory materials selected from the group consisting of alumina,beryllia, chromic oxide, feldspar, kaolin, silica, titania,

zinc oxide and zirconia for giving a body to the resistance element.

3. A cermet resistance element comprising a high temperature resistant,electrically nonconductive base, a film of fused glass fired onto asurface of the base, particles of at least one of the noble metalsselected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Rudispersed in the fused glass, and .5 to 40 percent by weight of Mn0dissolved in the fused glass and forming a part of the glass structure.

4. A cermet resistance element comprising particles of at least one ofthe noble metals in the amount of .5 to 20 percent by weight selectedfrom the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Rudispersed in a fused glass, .5 to 40 percent by weight of MnO dissolvedin the glass and structurally forming a part of the glass, and at leastone of the refractory materials selected from the group consisting ofalumina, beryllia, chromic oxide, feldspar, kaolin, silica, titania,zinc oxide and zirconia for giving a body to the resistance element.

5. A resistance element comprising a high temperature resistant,electrically nonconductive substrate, a film of glass bonded to asurface of the substrate, at least .5 percent by weight of MnO dissolvedin the glass and forming a structural part of the glass, and fineparticles of at least one of the noble metals selected from the groupconsisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in the glassin an amount of .5 to 20 percent by weight.

6. A resistance element comprising a high temperature resistant,electrically nonconductive base having fired thereonto a film ofresistance material comprising 40 to 99 percent by weight of asolidified glass, .5 to 40 percent by weight of MnO dissolved in theglass, and at least .5 to 20 percent by weight of one of the noblemetals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, OS,and Ru in finely divided form dispersed through the solidified glass inelectrically conductive relationship.

7. A resistance element comprising a body of solidified glass, at least.5 percent by weight of MnO structurally forming a part of the glass, aninert material for preventing the glass from flowing when fired to fusethe glass, and at least one of the noble metals selected from the groupconsisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely dividedform dispersed throughout the solidified glass.

8. A cermet resistance material consisting essentially of about 40 to 99percent by weight of a ceramic glass, at least .5 percent by weight ofone of the oxides of the noble metals selected from the group consistingof Ir, Os, and Ru in a finely divided state and dispersed in the glassas a conductive fraction, and .5 to 40 percent by weight of CuOdissolved in the glass and forming a structural part of the glass.

9. A cermet resistance material consisting essentially of about 40 to 99percent by weight of a ceramic glass, at least .5 percent by weight ofat least one of the oxides of the noble metals selected from the groupconsisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely dividedstate and dispersed in the glass as a conductive fraction, and .5 to 40percent by weight of a compound selected from the group consisting ofMnO and CuO dissolved in the glass and forming a structural part of theglass.

10. A resistance element consisting essentially of a high temperatureresistant, electrically nonconductive substrate, a film of glass bondedto a surface of the substrate, at least .5 percent by weight of CuOdissolved in the glass and forming a structural part of the glass, andfine particles of at least one of the oxides of the noble metalsselected from the group consisting of Ir, Os, and Ru dispersed in theglass as a conductive fraction in an amount of at least .5 percent byweight dissolved in the glass and forming a structural part of theglass.

11. A resistance element consisting essentially of a high temperatureresistant, electrically nonconductive substrate, a film of glass bondedto a surface of the substrate, at least .5 percent by weight of acompound selected from the group consisting of MnO and CuO dissolved inthe glass and forming a structural part of the glass, and fine particlesof at least one of the oxides of the noble metals selected from thegroup consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in theglass as a conductive fraction in an amount of at least .5 percent byweight.

12. A resistance element consisting essentially of a body of solidifiedglass, at least .5 percent by Weight of CuO dissolved in the glass andstructurally forming a part of the glass, an inert refractory materialfor preventing the glass from flowing when fired to fuse the glass, andat least one of the oxides of the noble metals selected from the groupconsisting of Ir, Os, and Ru in a finely divided form dispersedthroughout the solidified glass as a conductive fraction.

13. A resistance element consisting essentially of a body of solidifiedglass, at least .5 percent by Weight of a compound selected from thegroup consisting of MnO and CuO dissolved in the glass and structurallyforming a part of the glass, an inert refractory material for preventingthe glass from flowing when fired to fuse the glass, and at least one ofthe oxides of the noble metals selected from the group consisting of Ag,Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely divided form dispersedthroughout the solidified glass as a conductive fraction.

14. A method for improving the stability of a cermet resistance elementcomprising the steps of: adding .5 to 40 percent by weight of a compoundselected from the group consisting of MnO and CuO to a batch of rawmaterials employed in the preparation of a glass, heating the batch ofraw materials containing the compound to form a molten glass, dissolvingthe compound in the molten glass, fritting the molten glass by pouringthe molten glass into Water, removing the fritted glass from the water,grinding the fritted glass to a size of less than 325 mesh, and addingin a fine particle size .5 to 20 percent by weight of at least one ofthe oxides of the metals selected from the group consisting of Ag, Au,Pd, Pt, Rh, Ir, Os and Ru to the ground glass.

15. A method for improving the stability of a cermet resistance elementcomprising the steps of: admixing glassforming raw materials forpreparing a glass, heating the raw materials to form a molten glass,fritting the molten glass by pouring the glass into water, removing thefritted glass from the water, grinding the fritted glass to a size ofless than 325 mesh, adding .5 to 40 percent by weight of a compoundselected from the group consisting of Mn0 and CuO and .5 to 20 percentby weight of at least one of the oxides of the metals selected from thegroup consisting of Ag, Au, Pd, Pt, Rh, Ir, Os and Ru to the groundglass to form a composition, firing the composition to produce a ceramicresistance element having a stability of less than 1.0 percent.

References Cited UNITED STATES PATENTS 3,154,503 10/1964 Janakirama-Rao2525l4 LEON D. ROSDOL, Primary Examiner.

J. D. WELSH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE" OF CORRECTION Patent N003,324,049 June 6, 1967 Curtis Lo Holmes error appears in the abovenumbered pat- It is hereby certified that t the said Letters Patentshould read as ent requiring correction and the corrected below.

line 40, for "homegeneity" read homogeneity column 5, line 19, for"fllint" read flint column 6, lines 70 and 71, strike out "dissolved inthe glass and forming a structural part of the glass'h Column 3,

Signed and sealed this 28th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A CERMET RESISTANCE MATERIAL COMPRISING ABOUT 40 TO 99 PERCENT BYWEIGHT OF A CERAMIC GLASS, .5 TO 20 PERCENT BY WEIGHT OF AT LEAST ONE OFTHE NOBLE METALS SELECTED FROM THE GROUP CONSISTING OF AG, AU, PD, PT,RH, IR, OS; AND RU IN A FINELY DIVIDED STATE, AND .5 TO 40 PERCENT BYWEIGHT OF MNO2.
 15. A METHOD FOR IMPROVING THE STABILITY OF A CERMETRESISTANCE ELEMENT COMPRISING THE STEPS OF: ADMIXING GLASSFORMING RAWMATERIALS FOR PREPARING A GLASS, HEATING THE RAW MATERIALS TO FORM AMOLTEN GLASS, FRITTING THE MOLTEN GLASS BY POURING THE GLASS INTO WATER,REMOVING THE FRITTED GLASS FROM THE WATER, GRINDING THE FRITTED GLASS TOA SIZE OF LESS THAN 325 MESH, ADDING .5 TO 40 PERCENT BY WEIGHT OF ACOMPOUND SELECTED FROM THE GROUP CONSISTING OF MNO2 AND CUO AND .5 TO 20PERCENT BY WEIGHT OF AT LEAST ONE OF THE OXIDES OF THE METALS SELECTEDFROM THE GROUP CONSISTING OF AG, AU, PD, PT, RH, IR, OS AND RU TO THEGROUND GLASS TO FORM A COMPOSITION, FIRING THE COMPOSITION TO PRODUCE ACERAMIC RESISTANCE ELEMENT HAVING A STABILITY OF LESS THAN 1.0 PERCENT.